Six US soldiers and three Afghan troops have been killed in fighting in eastern Afghanistan, Nato officials have said.
This year has been one of the deadliest for coalition forces
Militants ambushed a patrol of Afghan soldiers and US troops from Nato's International Security Assistance Force (Isaf) in Nuristan province.
The ambush is one of the costliest for US forces this year, already the deadliest for the US since it helped overthrow the Taleban in 2001.
Eight US troops and 11 Afghans were also wounded, Isaf officials said.
The Taleban said they carried out the attack, which took place on Friday.
The rebels attacked from several positions simultaneously with small arms fire and rocket-propelled grenades as the patrol returned from a meeting with village elders, said Isaf spokesman Brig Gen Carlos Branco.
A US military spokesman described the attack as a "complex ambush".
The latest casualties bring US fatalities this year in Afghanistan to 101.
Fighting between militants and international forces has intensified in the past two years as the Taleban have mounted a resurgence.
Attacks have increased in remote Nuristan province, on the border with north-west Pakistan, which has also seen increasing violence from pro-Taleban militants.
But Brig Gen Branco told the BBC that despite threats from Taleban leader Mullah Omar to spread the fighting to the north, it was still "fairly safe and stable".
There are currently more than 50,000 foreign soldiers in Afghanistan.
About 40,000 are under the command of Isaf, the rest form a coalition under US direction.